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Physics Astrophysics

astro-ph Watch Astrophysics

Wednesday 1 July

Astrophysics of Galaxies

Fractional-Dimension Gravity and the Milky Way Galaxy

Gabriele U. Varieschi

In this work, we focus our analysis of Fractional-Dimension Gravity (FDG) on our home galaxy, the Milky Way (MW), by using the latest Gaia DR3 data as well as previous rotation curve (RC) data for this galaxy. FDG is an alternative gravitational model (previously known as Newtonian Fractional-Dimension Gravity - NFDG) which does not require the dark matter (DM) paradigm. The MW is studied here with the methods of FDG and its observed rotation curves are successfully reproduced by using a variable fractional dimension $D\left (R\right)$, following previous studies of several other galaxies which were analyzed with the same methodology. An alternative dimension function $D_{m}\left(R \right)$, based on the mass-dimension field equation, was also used and yielded less accurate fits to the experimental data. In addition, we also considered possible implications of the FDG metric, based on the presence of additional weights, on the structure of Special Relativity (SR) for spacetimes with fractional dimension. One notable, but very speculative outcome of this analysis is the possibility of an effective superluminal motion in galactic regions where the space dimension is $D<3$.
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Cosmology and Nongalactic Astrophysics

Secondary Production of Photons from ALP Dark Matter interacting with a Cosmological Magnetic Field

Abdias Aires, Robert Brandenberger and Ashu Kushwaha

Under the assumption that dark matter is a coherently oscillating pseudoscalar field coupled to electromagnetism by the usual Chern-Simons term, we study the production of secondary photons from dark matter fluctuations coupled to a pre-existing magnetic field, taking into account the spectral distribution of the magnetic field. Specifically, we apply the formalism to the case of a large-scale magnetic field generated previously via a parametric resonance instability due to the same Chern-Simons coupling. However, our analysis is applicable to any spectrum of cosmological scale magnetic field fluctuations present at the time of recombination. We show that obtaining a sufficiently large flux of photons in the Lyman-Werner frequency range is consistent with constraints from CMB and X-ray observations.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Neutron stars as thermometers for reheating induced dipole dark matter

Sahabub Jahedi

We investigate the electromagnetic interactions of dipole dark matter (DM) within an effective field theory framework, considering both standard and non-standard cosmological scenarios. We first study the prospects of DM production via both the freeze-out and freeze-in mechanisms within the standard radiation-domination. We then investigate how the viable DM parameter space is modified in a non-standard cosmological scenario due to entropy dilution during reheating. Existing constraints on the parameter space are discussed, and we highlight the discovery potential of future direct detection experiments to probe these scenarios. We further investigate the implications of neutron star heating for dipole DM. Due to the momentum-dependent nature of the interaction, dipole DM is captured efficiently by neutron stars, thereby making neutron star heating a sensitive probe of the dipole DM parameter space.
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Cosmology and Nongalactic Astrophysics

Lensing-Reconstructed Dark Matter-Intracluster Medium Coherence as a Probe of Cluster Dynamical State: Application to HSTFF, RELICS, and CLASH Clusters

Giulia Cerini, Sayan Saha, Jacqueline McCleary et al. (+13 more)

We present the first application of Fourier-space coherence analysis between the lensing-reconstructed projected mass distribution and the X-ray-emitting intracluster medium to a sample of 49 observed galaxy clusters. Using publicly available HST convergence maps from the Hubble Frontier Fields, CLASH, and RELICS programs, together with Chandra X-ray imaging, we measure the scale-dependent coherence between the dark-matter-dominated surface mass density and the hot baryonic gas. We use the coherence length, l_CR, defined as the scale above which the two maps remain at least 90% coherent, as a diagnostic of cluster dynamical state. Across the sample, dynamically relaxed systems exhibit high coherence over a broad range of scales and small l_CR/r500, while disturbed and merging systems show a loss of coherence on intermediate and small scales, yielding larger l_CR/r500. The inferred coherence lengths show sensitivity to lens-model assumptions and to the heterogeneous extent of the available convergence maps. Nevertheless, the coherence signal remains physically interpretable and provides a stringent measure of dark-matter-gas alignment. Applying a conservative threshold, l_CR/r500 < 0.2, we find that only 16% of the sample is relaxed; this fraction rises to 41% for a more permissive threshold of l_CR/r500 < 0.4. Relative to previous X-ray and morphological classifications, we find a 24% disagreement, with the coherence method identifying more systems as dynamically disturbed. These results demonstrate that lensing-X-ray coherence provides a complementary, scale-resolved probe of cluster dynamical state, while highlighting the need for homogeneous, wide-field weak-lensing maps to control reconstruction and field-of-view systematics.
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All authors Giulia Cerini, Sayan Saha, Jacqueline McCleary, Eric Habjan, Nico Cappelluti, Priyamvada Natarajan, Sabina Khizroev, Jason Rhodes, Eric Huff, Nicole Chidester, Maya Amit, Andrew Robertson, Bryanne McDonough, Elena Bellomi, Erwin T. Lau, John ZuHone

Solar and Stellar Astrophysics

Stark-Broadened Profiles for Ionized Helium Lines Using Computer Simulations

Patrick Tremblay, Alain Beauchamp and Pierre Bergeron

We present new and improved calculations of Stark-broadened profiles for ionized helium, a key ingredient in the spectroscopic analysis of helium-atmosphere DO white dwarfs. Our approach builds upon the computer simulation framework previously developed for neutral helium, which fully accounts for the dynamical interactions of both ions and electrons with the emitting helium atom. We extend this theoretical formalism by relaxing the assumption of straight-line trajectories for the perturbing particles (electrons and ionized helium) and adopting the hyperbolic trajectories appropriate for their interaction with a charged emitter, thereby accounting for their dynamical influence on the line-broadening process. In this exploratory study, we focus on the He II 4686 line, the strongest absorption feature observed in the spectra of DO white dwarfs. We present the resulting Stark profiles and perform a detailed comparison with those available in the literature.
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High Energy Astrophysical Phenomena

AI-enabled gravitational-waves searches for binary neutron stars at optimal sensitivity

Bhavya Gupta, Deep Chatterjee, William Benoit et al. (+7 more)

Gravitational Waves (GWs) represent the newest window of astronomy, furthering our understanding of compact objects like black holes and neutron stars in the Universe. The signal from two merging neutron stars is especially interesting since it brings the prospect of concordant electromagnetic and neutrino emissions. Such multi-messenger observations have a transformational impact on fundamental physics, nuclear matter, astrophysics, and gravity. It was first witnessed in 2017 with the detection of the binary neutron star (BNS) merger GW170817. However, searching for BNS signals in real-time in the LIGO-Virgo-KAGRA (LVK) GW detectors presents a computational challenge, as the data streaming out must be matched against $\sim$ million reference waveforms, which requires up to a thousand CPU cores. We present a different approach using neural networks to learn the presence of a signal in the data. Our algorithm, called Aframe, was deployed in the LVK's fourth observing run and was the first artificial intelligence (AI)-enabled search to detect multiple binary black holes (BBHs) live. In this work, we demonstrate that the approach extends to the lower-mass BNS regime, and is the first AI-enabled search that achieves sensitivity comparable to matched-filter pipelines at lower computational and latency costs. The challenge of the longer-duration BNS signals is addressed by heterodyning the data, following which the network architecture used for BBHs is sufficient to distinguish signal versus background. We also show that this analysis requires a single non-flagship GPU for online deployment. Furthermore, the design and adoption of inference-as-a-service tools allow rapid offline analysis using a distributed pool of GPU resources. Hence, aside from the use case of rapid online data analysis, we also establish the use of Aframe for efficient archival data analysis.
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All authors Bhavya Gupta, Deep Chatterjee, William Benoit, Ethan Marx, Christina Reissel, Seiya Tsukamoto, Kyungseop Yoon, Michael W. Coughlin, Philip Harris, Erik Katsavounidis

High Energy Astrophysical Phenomena

Constraining the near-source relativistic wind medium using Fast Radio Burst circular polarization data

Om Gupta, Pawan Kumar and Paz Beniamini

Fast Radio Bursts (FRBs) exhibit diverse spectro-temporal characteristics, which can probe vital propagation and source physics via Stokes polarimetry. We investigate whether the circular polarization (Stokes $V$) observed in some bursts is produced by Faraday conversion in the near-source wind of magnetars rather than being intrinsic to the source. Our calculation includes the increase in the effective mass of $e^\pm$ in the presence of the FRB wave. We find that Faraday conversion in the magnetar wind can explain the broad range of observed circular polarization in FRBs, including its frequent non-detection. Observationally derived upper limits on $V$ provide stringent constraints on the wind luminosity, magnetization, bulk Lorentz factor, and effective particle mass when ions are present. When available, frequency resolved Stokes spectra offer direct estimates of the wind environment. The Stokes parameters can undergo rapid oscillations with frequency in the high-wind/low-FRB-luminosity regime, resulting in Stokes-V depolarization. Bursts with significantly lower luminosities than typical FRBs can also develop measurable circular polarization, within the model framework. Additionally, separate zones are favored for significant circular polarization and rotation measure, when the model is applicable. The model constrains instantaneous wind parameters for several sources, including FRB 20201124A, FRB 20180301A, and SGR 1935+2154. This work represents the first instance in which properties of winds from compact objects associated with FRBs are inferred from polarization data.
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High Energy Astrophysical Phenomena

X-ray polarization in magnetized neutron stars

Tanuman Ghosh and Shiv Sethi

X-ray polarimetry has opened a new window into understanding the physics around magnetized compact objects. IXPE detection of linear polarization from such systems has prompted a new spurt of theoretical modeling. Our study is based on the dominant paradigm that the observed polarization arises from the scattering of photons around highly magnetized systems. Our main focus is the dependence of the polarization of the scattered light on properties of the incoming light, i.e., geometry and the polarization state, and the determination of the spectral shape of the polarized light for a wide range of magnetic field strengths. We also analyze the impact of vacuum birefringence on photon polarization. We show that, generically, we expect a higher linear degree of polarization from magnetars as compared to normal pulsars, which is in agreement with IXPE observations. Under some conditions, our study helps to understand the observed degree of polarization from normal pulsars and low-magnetized neutron stars and their spectral dependence. However, we cannot conclusively explain the spectral shape of the observed polarization for magnetars using only a single component emission from scattering in a strong magnetic field. This probably points to the system being more complex, e.g., multi-component, than our study allows for. Upcoming X-ray polarimeters with broader energy coverage could probe some of our other predictions, e.g., the spectral shape of the polarized light close to the resonance frequency.
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High Energy Astrophysical Phenomena · Cross-listed from hep-ph

Electron stability constrains neutrino time delays

Mauricio Bustamante, José Manuel Carmona, José Luis Cortés et al. (+2 more)

Superluminal neutrino propagation, induced by Lorentz-invariance violation (LIV), is strongly constrained by vacuum pair emission, $\nu \to \nu + e^- + e^+$, a process ordinarily forbidden, which rapidly degrades the energy of high-energy neutrinos. Consequently, observable neutrino time delays are often preferentially associated with subluminal propagation, prompting LIV interpretations of claimed time delays between high-energy cosmic neutrinos and gamma rays. However, this expectation is at odds with the observed stability of high-energy electrons. The same Lorentz-violating correction associated with subluminal neutrino propagation opens the overlooked complementary decay channel $e^- \to e^- + \nu + \bar{\nu}$, leading to electron instability. We derive constraints on LIV from recent observations of TeV–PeV astrophysical electrons. These electron stability limits rule out LIV invoked to explain delays of high-energy cosmic neutrinos. Consequently, neutrino time delays are constrained on both the superluminal and subluminal sides. Therefore, observable delays require either purely astrophysical origins, a realization of LIV that affects all particle species equally, or physics beyond the standard effective-field-theory framework.
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All authors Mauricio Bustamante, José Manuel Carmona, José Luis Cortés, Ardit Gkioni, Maykoll A. Reyes

Astrophysics of Galaxies

IRIS: Deciphering Spectral-Line Imagery of the Galactic Center by Machine-Learning on Simulations

B. L. DuBois, Cara Battersby, Jonah C. Baade et al. (+11 more)

In understanding the 3D structure of the Milky Way's Central Molecular Zone (CMZ), we are limited by our edge-on perspective. Towards addressing this problem, we introduce Imagery Reversion Informed by Simulation (IRIS). IRIS is a novel machine-learning code base featuring a deep convolutional neural network (CNN), which we have designed to translate edge-on observations of our Milky Way Galaxy into top-down images by training on data generated from AREPO galaxy simulations and synthetic observations of those simulations. We develop a large custom dataset on which we train our bespoke model, and then test the trained model on synthetic data to probe the potential of this machine-learning method, which we call supervised reversion. We then apply our trained model to real observations from the SEDIGISM 13CO(2-1) survey, yielding new top-down views of our CMZ. Though our SEDIGISM reversions are not fully consistent across model training runs, we posit that this lack of convergence can be alleviated by expansion of the training dataset. We argue that these results represent a strong proof-of-concept for the use of supervised reversion to decipher our CMZ's 3D structure. Crucial in generating our training dataset's 100k synthetic observations, we introduce IRIS Synthetic Observation (IRIS-SO), a new GPU-accelerated and fully differentiable code implemented in PyTorch for the non-LTE synthetic observation of spectral lines and dust. We find that IRIS-SO provides up to 10,000x speedups in comparison to the synthetic-observation code RADMC-3D. We release all the IRIS code open-source at https://github.com/bldubois/IRIS.
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All authors B. L. DuBois, Cara Battersby, Jonah C. Baade, Dani R. Lipman, H Perry Hatchfield, Jack Sullivan, Russell Bentley, Stefan Reissl, Ralf S. Klessen, Victor F. Ksoll, Mattia C. Sormani, Zi-Xuan Feng, Adam Ginsburg, Robin Tress

High Energy Astrophysical Phenomena

A possible high-redshift origin for the short GRB 061201: implications of a compact binary merger beyond cosmic noon

E. Troja, B. O'Connor, Y.-H. Yang et al. (+4 more)

Short gamma-ray bursts (GRBs) at redshift z>2 remain exceptionally rare, yet they are crucial for tracing compact binary mergers in the early Universe and understanding their role in the production of r-process elements. GRB 061201 is an unusual and still debated event: although its optical afterglow was accurately localized, no secure coincident host galaxy was identified, and the proposed associations with nearby galaxies all require a large separation between the GRB and its birth site. In this work, we revisit GRB 061201 and argue that the observations are more naturally explained if the burst occurred within a faint F322W2~28.4 AB mag galaxy at z>2. By combining constraints from the afterglow and deep near-infrared imaging from JWST, we show that a distant origin provides a coherent explanation of the burst phenomenology. If confirmed, GRB 061201 would represent one of the most distant short GRBs known, extending the observed compact merger population to an epoch when the Universe was only about two billion years old.
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All authors E. Troja, B. O'Connor, Y.-H. Yang, T. M. Gaudin, M. Yadav, N. Passaleva, S. Dichiara

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Axion Misalignment Across First-Order Phase Transitions

Galymzhan Baltabay, Francesco D'Eramo and Ville Vaskonen

When the axion mass is generated during a first-order phase transition and becomes non-vanishing only inside expanding true-vacuum bubbles, the standard picture of misalignment production is qualitatively modified. Using lattice simulations in an expanding universe, we study dark matter production within such a framework and identify two distinct regimes. For rapid transitions, the onset of oscillations is delayed until bubble percolation, enhancing the relic abundance. For slower transitions, spatial gradients generated by expanding bubbles suppress the effective misalignment angle through the bubble misalignment mechanism. We derive a semi-analytical expression for the relic density that provides a unified description of both regimes and accurately reproduces the simulation results. Finally, we show how this mechanism also modifies isocurvature perturbations and the small-scale matter power spectrum, with important implications for axion minicluster formation.
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Astrophysics of Galaxies

The fingerprint of primordial mass segregation on the tidal tails of star clusters

S. Mojtaba Ghasemi, Hosein Haghi, Mohammad Mansoury et al. (+3 more)

We investigate the effect of primordial mass segregation (PMS) in shaping the tidal tail structures of star clusters, searching for any trace of PMS on the tails at both early and late evolutionary stages. Through N-body simulations, we analyze clusters with two different degrees of PMS at various Galactocentric distances (R_G), considering two black hole retention scenarios. Our findings reveal that PMS influences early cluster expansion and the formation of tidal tails with a bottom-heavy stellar mass function, this being more pronounced at smaller R_G but diminishes over time. Primordially segregated clusters exhibit denser, unified, and longer tail structures compared to non-segregated clusters. The mean stellar mass distribution along the tails shows distinct patterns for primordially segregated and non-segregated clusters, converging at later evolutionary stages. The retention of stellar remnants has a weak impact on the mean mass distribution along the tails and on its morphology. We find that although mean mass differences persist along the tidal tails, the rate of change in primordially mass-segregated clusters eventually converges with that of non-segregated clusters, suggesting that the influence of primordial mass segregation on the tidal tails gradually diminishes over the course of cluster evolution.
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All authors S. Mojtaba Ghasemi, Hosein Haghi, Mohammad Mansoury, Akram Hasani Zonoozi, Pouriya Miri, Pavel Kroupa

Astrophysics of Galaxies

Extreme outflow velocities and weak UV emission lines indicate quasars shedding their dust cocoons

Guozhen Ma, Stefan J. Geier, Johan P. U. Fynbo et al. (+11 more)

The recently discovered low-ionisation broad absorption line (LoBAL) quasar GQ 1309$+$2904 is unusual due to its very broad, highly blueshifted absorption troughs and an absence of broad emission lines except for ${\mathrm{H} \alpha}$. In this paper, we present observations of six quasars that appear very similar to GQ 1309$+$2904 in the rest-frame ultraviolet (UV). We measure the systemic redshifts of these quasars to be $z\approx$ 2.07–3.28 from detected ${\mathrm{H} \alpha}$ emission lines. We confirm that all targets are quasars with highly blueshifted BALs possessing high-speed outflows with velocities up to $\sim 0.16\,c$, and five of them are confidently identified as LoBAL quasars. Based on ${\mathrm{H} \alpha}$ emission, black hole masses and Eddington ratios of these quasars are $M_{\mathrm{BH}} \approx 10^{8.7}$–$10^{9.4}\,M_{\odot}$ and $L_{\mathrm{bol}} / L_{\mathrm{Edd}} \approx$ 0.14–0.34, indicating that their central black holes are very massive and active. Every quasar in our sample exhibits a very flat or reddened continuum. The spectral shapes of three objects are well-fitted by a normal quasar composite reddened by a Small-Magellanic-Cloud-like (SMC-like) extinction curve, while the other three require a steeper extinction law. Broad-band ($BVR$) polarimetry for two of the latter group (plus GQ 1309$+$2904) reveals their low polarisations, consistent with low inclination (more face-on) angles. We propose that these objects are weak emission-line quasars (WLQs) observed through the disc wind, caught emerging from their dust cocoons. As quasars shed their cocoons, dust grains in the disc wind are shattered into smaller particles, producing the UV-steeper extinction curve observed along the outflow. We present a schematic illustration of this shedding process that can account for the peculiar spectral features observed in our sample.
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All authors Guozhen Ma, Stefan J. Geier, Johan P. U. Fynbo, Lise Christensen, Andrei Berdyugin, Rasmus Frederiksen, Kasper E. Heintz, Phillip D. Henriksen, Jens-Kristian Krogager, Cédric Ledoux, Vilppu Piirola, Palle Møller, Simone Vejlgaard, Hyunseop Choi

Instrumentation and Methods for Astrophysics

TEQUILA: Mechanism-free polarimetry for astronomy

Alan M. Watson and Noémie Globus

TEQUILA (Transient Event $Q$, $U$, and $I$ Light Analyzer) is an optical imaging polarimeter developed for the second Nasmyth port of the 1.3-m COLIBRÍ altitude-azimuth telescope at Observatorio Astronómico Nacional in San Pedro Mártir, México (OAN-SPM). TEQUILA uses a CMOS sensor with an on-chip wire-grid micro-polarizer array to obtain simultaneous, single-exposure measurements of the Stokes parameters $I$, $Q$, and $U$ without moving optical components. This mechanism-free instrument, built entirely from commercial components, delivers seeing-limited imaging in a fixed optical band and is optimized for early-time follow-up of transient sources, including gamma-ray burst afterglows, blazars, and variable young stellar objects. In this paper, we describe the scientific motivation, the instrument design and implementation, the calibration, and initial science results. Sensor characterization reveals a polarimetric structure in the flat field and a low quantum efficiency, which we estimate to be approximately 17%, including losses introduced by the micro-polarizer array. For point sources, TEQUILA achieves absolute polarimetry with RMS uncertainties of 0.15% in pupil-tracking observations and 0.20% in field-tracking observations. In pupil-tracking mode, the observed RMS is fully explained by the measurement and standard-star uncertainties, with no evidence for an additional calibration term. In contrast, field-tracking observations require an additional calibration uncertainty of approximately 0.10%. Calibration for resolved-source polarimetry remains in progress.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Impact of Spacecraft Orbit Uncertainties and Velocity Mismodeling on the LISA Gravitational-Wave Response

Lorenzo Speri, Olaf Hartwig, Waldemar Martens et al. (+5 more)

The Laser Interferometer Space Antenna (LISA) is a space-based gravitational wave observatory that consists of three spacecraft in a near-equilateral triangular formation. The spacecraft orbits are typically assumed to be perfectly known in LISA data analysis studies, but in reality, the orbit determination process introduces uncertainties in the spacecraft positions and velocities. In this work, we investigate how these uncertainties propagate into the LISA detector output and the impact of neglecting the spacecraft velocities. We quantify these errors in the knowledge of the LISA response using mismatches and discuss the implications for gravitational wave data analysis. We find that spacecraft orbit uncertainties impact the LISA response knowledge at high frequencies with worst mismatch below $10^{-7}$. The effect of neglecting the spacecraft velocities is largest at frequencies around $10^{-4}$ Hz with mismatches of order $10^{-4}$. For a galactic binary with frequency $10^{-4}$ Hz and SNR=200 observed for one year, we find that neglecting the spacecraft velocities in the response leads to less than 1-$\sigma$ biases in the parameter estimates. This work provides the first characterization of how errors in the LISA gravitational wave response propagate from gravitational wave strain through detector output to estimated parameters.
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All authors Lorenzo Speri, Olaf Hartwig, Waldemar Martens, Oliver Jennrich, Eric Joffre, Michele Armano, Martin Hewitson, Nora Lützgendorf

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

No Evidence for Superradiant Axions in LIGO-Virgo-KAGRA GWTC-5 Binary Black Hole Spins

Orion Ning, Benjamin R. Safdi and Catherine Welch

The quantum chromodynamics (QCD) axion and axion-like particles may form bound clouds around spinning black holes (BHs) when their Compton wavelength is comparable to the BH gravitational radius, depleting the BH spin through what is known as a $\textit{superradiance}$ instability. Using binary BH (BBH) spin measurements obtained from the LIGO-Virgo-KAGRA GWTC-5 catalog, the most extensive public BBH catalog to date containing $N=257$ mergers with BH masses spanning roughly $5$-$135$ $M_\odot$, we perform a hierarchical Bayesian analysis in the context of a BH spin population model to constrain ultralight axions. The presence of axions at a given mass would imprint a unique signature in the observed mass-spin relation relative to the formation distribution. We find no evidence for axions across more than two decades in mass, excluding axion masses $1.7 \times 10^{-14} \, {\rm eV} \lesssim m_a \lesssim 3.3 \times 10^{-12} \, {\rm eV}$ at 95% confidence. Because prior superradiance bounds in this range derive from X-ray spin measurements with substantial modeling systematics, this result represents one of the strongest robust lower bounds on the QCD axion mass.
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Earth and Planetary Astrophysics

Aerosols and hydrocarbons in the atmosphere of a white dwarf planet

Ryan J. MacDonald, Christopher E. O'Connor, Victoria A. Boehm et al. (+15 more)

Most stars, including our Sun, will one day evolve into red giants and, subsequently, white dwarfs. Several planet candidates have recently been identified orbiting white dwarfs, demonstrating that planets can survive the stellar post-main-sequence stage intact. Little is known about the atmospheric composition of post-main-sequence planets, with the most evolved transiting planets with atmospheric detections to date orbiting subgiants. Here we report an atmospheric detection for the white dwarf planet WD 1856 b, achieved through transmission spectroscopy with the JWST NIRSpec PRISM. Our 0.5-5.0 $\mu$m spectrum reveals the presence of hydrocarbons (odds ratio of $167:1$ to $5377:1$, with $\mathrm{CH}_4$ preferred at $17:1$ to $30:1$), aerosols ($2 \times 10^5:1$ to $2 \times 10^6:1$), and thermal emission from the planetary nightside ($2 \times 10^{63}:1$ to $2 \times 10^{73}:1$). Our spectral analysis constrains WD 1856 b's mass to $4.3$ to $10.9 \mathrm{M}_J$, finds a carbon-enriched atmosphere (with a $\mathrm{CH}_4$ abundance of $\approx 7\%$), and an effective temperature exceeding the expected planetary equilibrium temperature ($390$ to $412 \, \mathrm{K}$ vs. $160 \, \mathrm{K}$). Based on cooling models, these results suggest that WD 1856 b underwent a migration-related reheating event $3.0$ to $5.5 \, \mathrm{Gyr}$ into the white dwarf phase, consistent with post-main-sequence tidal evolution to the present-day $0.02 \, \mathrm{au}$ circular orbit. Our results provide a window into the ultimate fate of giant planets orbiting stars with masses similar to our Sun.
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All authors Ryan J. MacDonald, Christopher E. O'Connor, Victoria A. Boehm, E. M. May, David K. Sing, Elijah Mullens, L. C. Mayorga, Trevor O. Foote, Simon Blouin, Logan A. Pearce, Nikole K. Lewis, Jeff Valenti, Natasha E. Batalha, Maura Lally, Joshua D. Lothringer, Mark S. Marley, Ishan Mishra, Susan E. Mullally

Earth and Planetary Astrophysics

Discovery of an Inflated Hot Neptune and Its Formation from Jovian Mass Loss

Grant C. Weldon, Samuel W. Yee, Bradley M. S. Hansen et al. (+17 more)

The production of Neptune-like planets with orbital periods of 3–6 days is challenging for conventional models of high-eccentricity migration. We present the discovery and characterization of TOI-2195~A~b, an inflated hot Neptune ($P = 4.16$ days, $m_p= 1.46M_{\rm Nep},\,R_p = 0.79R_{\rm J}$) orbiting an early K-type star with a wide binary companion at $\sim 600$~au. Detection of the Rossiter-McLaughlin effect at $\sim2.6\sigma$ confidence with Magellan/PFS reveals the planet is likely on a near-polar orbit with a sky-projected stellar obliquity $\lambda = {109^{+35}_{-53}} ^{\circ}$. We perform coupled dynamical and structural modeling that reproduces the observed characteristics of the system. We show that the planet may have originated as a cold, Jovian planet that was excited to high eccentricities via the stellar Eccentric Kozai-Lidov (EKL) mechanism, where it lost up to $\sim90\%$ of its mass via Roche lobe overflow during close periastron passages, enabling rapid tidal migration and radius inflation due to tidal heating. TOI-2195 A b provides a test for planetary migration theories, and our simulations suggest that puffy hot Neptunes originated as more massive Jovians that underwent mass loss during high-eccentricity migration.
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All authors Grant C. Weldon, Samuel W. Yee, Bradley M. S. Hansen, Smadar Naoz, Joel D. Hartman, Joshua N. Winn, R. Paul Butler, Jeffrey D. Crane, Phil Evans, Tianjun Gan, Steve B. Howell, Michelle Kunimoto, David Osip, David Rapetti, Stephen A. Shectman, Keivan G. Stassun, Johanna K. Teske, Roberto Zambelli, George Zhou, Carl Ziegler

Cosmology and Nongalactic Astrophysics

How I stop worrying about non-universality and $b_\phi$: Constraining local $f_{\rm NL}$ with $b_\phi$ priors from HOD posteriors

Jiaxi Yu and Nhat-Minh Nguyen

Local primordial non-Gaussianity (local PNG) induces a scale-dependent contribution to galaxy clustering proportional to $f_{\rm NL}\,b_\phi$, where $f_{\rm NL}$ is the local PNG amplitude and $b_\phi$ encodes the galaxy response to a long-wavelength primordial potential perturbation. Uncertainty in $b_\phi$ is the dominant obstacle to precise, robust constraints on $f_{\rm NL}$ from galaxy surveys. We translate small-scale clustering constraints on the galaxy–halo connection into priors on $b_\phi$: sampling the posterior of a halo occupation distribution (HOD) model fit to the DESI EDR, we generate mocks from which we measure $b_\phi$ and construct its prior. Validating against additional mocks with different local PNG amplitudes, we show that the method recovers unbiased $f_{\rm NL}$, even in the presence of assembly bias.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Can Primordial Black Holes Be Seeds for Early Galaxies in Models Satisfying the Covariant Entropy Bound?

Sidan A, Tom Banks and Willy Fischler

We argue that cosmological models obeying the Covariant Entropy Bound (CEB) mathematically favor states with no localized excitations or one large black hole containing all the energy in a constrained initial state. In order to get a long radiation-dominated era, one must postulate that at a very early time, most horizon volumes of the universe contained tiny black holes that decayed into radiation. A previous work by two of the authors showed that such a scenario could fit the data on the Cosmic Microwave Background (CMB). In order to account for dark matter, we also postulate some random black holes of at least horizon size at that time. A reasonable distribution of such primordial black holes can account for all of dark matter as well as the early galaxies seen by the James Webb Space Telescope. Some of the dark matter may also be in Planck-scale remnants of the decaying black holes. We describe our model both in terms of approximate solutions to General Relativity and a speculative quantum gravity model whose hydrodynamics matches the flat $p = \pm \rho$ FRW model that saturates the CEB.
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High Energy Astrophysical Phenomena

Pulsar Science with the SKAO

Bhal Chandra Joshi, Aris Karastergiou and Marta Burgay

The large instantaneous sensitivity, wide frequency coverage and flexible observation modes, with large number of beams in the sky, are the main features of the SKA observatory's two telescopes, the SKA-Low and the SKA-Mid. Owing to these capabilities, the SKAO telescopes are going to be a game-changer for radio astronomy in general and pulsar astronomy in particular. Eleven chapters in this book describe their impact on different areas of pulsar science. In this overview article each chapter is briefly summarised and the inter-relationship between different pulsar science use cases are explored: new deep surveys, covering the Galactic field, globular clusters and the Galactic centre, will discover thousands of new pulsars; these will form the backbone for studies of neutron star physics and of their environments. The enhanced understanding provided by these studies will feed into the main contributions to fundamental physics from pulsar astronomy: testing relativistic gravity, studying gravitational waves in the nano-Hz regime and studying the equation of state of nuclear matter. Synergies with other science cases are also highlighted throughout this overview.
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2607.01288 · 1 Jul · 13 pages, 2 figures, Published in Advancing Astrophysics with the SKA II (AASKAII), 2026 (arXiv:2606.20366). Report number AASKAII/Joshi01. Advancing Astrophysics with the SKA II (AASKA II) outlines the transformative scientific advances that will be enabled by the SKA telescopes. An earlier version of this chapter was published in The Open Journal of Astrophysics with arXiv ID: arXiv:2512.16152

Abstract PDF $PLSR ×6$GALAC ×2$TSCP ×2$GRAV ×1 +4

High Energy Astrophysical Phenomena

Beta-Particle Transport and Thermalization in Kilonova Ejecta with Detailed Atomic Microphysics

Zachary L. Andalman, Christopher L. Fryer, Christopher J. Fontes et al. (+2 more)

When two neutron stars collide, they eject material containing heavy nuclei formed by the rapid neutron capture process ($r$-process). As these nuclei decay, they power a bright optical/near-infrared transient known as a kilonova (KN). Modeling KN emission is a complex problem involving atomic opacities, radiation transport, and heating powered by the thermalization of radioactive decay products like $\gamma$-rays, $\alpha$-particles, and $\beta$-particles. For heating by $\gamma$-rays, many KN modeling codes do full radiation transport calculations. However, heating by $\alpha$- and $\beta$-particles relies on simplified descriptions of collisions and transport, and remains an important source of uncertainty in KN models. In this paper, we study the thermalization and transport of $\beta$-particles. To study thermalization, we use evaluated atomic physics data to estimate per-species contributions to energy deposition, scattering, and electron impact ionization, which we make available online. To include non-local effects, we develop a fully relativistic framework for charged particle transport in a spherically symmetric, homologously expanding ejecta, considering two limiting magnetic-field geometries. Non-local energy deposition and escape reduce thermalization efficiency, especially in the innermost and outermost ejecta, lowering the ejecta temperature and ionization state compared to local deposition models. Coulomb scattering partially offsets these effects by trapping particles at intermediate times $\sim 3-30$ days. Ionization by secondary electrons significantly enhances the overall ionization rate. We provide analytic prescriptions for the spatially dependent thermalization efficiency for use in future light-curve calculations. Our results demonstrate that evaluated atomic data and charged-particle transport should be incorporated into the next generation of KN models.
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All authors Zachary L. Andalman, Christopher L. Fryer, Christopher J. Fontes, Matthew R. Mumpower, Ryan T. Wollaeger

Cosmology and Nongalactic Astrophysics

Intertwined Constraints in Extended Cosmologies: Dark Energy, Curvature, Neutrinos, and Inflation

William Giarè, Dong Ha Lee and Eleonora Di Valentino

We present a systematic reassessment of cosmological constraints beyond $\Lambda$CDM by progressively relaxing the assumptions underlying Dark Energy (DE), Curvature, Neutrinos, and Inflation. Using the latest CMB data together with DESI BAO and different SN catalogues, we show that the preference for dynamical DE persists across all the extended cosmologies considered. $\Omega_k$ remains compatible with flatness, despite a mild $2.2\sigma$ preference for $\Omega_k>0$ that is substantially degraded in dynamical DE extensions. Constraints on $N_{\rm eff}$ are broadly consistent with $N_{\rm eff}=3.04$, while cosmological upper limits on the total neutrino mass vary substantially across the cosmologies explored, ranging from $\sum m_\nu\lesssim 0.06$ eV to $\lesssim 0.2$ eV. We quantify both the preference for the mass ordering and the apparent tension between cosmology and oscillation experiments, showing that they are strongly framework dependent. We find no evidence for inflationary tensor modes, with $r\lesssim 0.035$. Constraints on the spectral index $n_s$ show significant model dependence. Allowing for the scalar runnings produces a mild shift toward $\alpha_s>0$ and $\beta_s>0$ that can reabsorb the preference for larger $n_s$ found in small-scale CMB data, although both $\alpha_s$ and $\beta_s$ remain consistent with zero at $\sim 1.5\sigma$. We highlight the implications for slow-roll inflation and benchmark models. None of the extensions considered here can resolve the $H_0$ tension. We discuss the implications for $\Omega_m$ and $S_8$. Overall, dynamical DE is the only significant deviation from $\Lambda$CDM and has the strongest impact on the inferred conclusions in the other sectors of the model.
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Instrumentation and Methods for Astrophysics

TIME Commissioning Observations: II. On-sky Characterization and the 2D Map Data Processing Pipeline

Benjamin J. Vaughan, Abigail T. Crites, Dongwoo T. Chung et al. (+24 more)

The Tomographic Ionized-carbon Mapping Experiment (TIME) is a line intensity mapping (LIM) instrument that is designed to observe the power spectrum of the [CII] $158$~$\mu$m emission line during the Epoch of Reionization. TIME completed a commissioning run in 2022 at the Arizona Radio Observatory onboard the 12-M Radio Telescope at Kitt Peak, where it observed galactic sources for the first time. In this paper we report on an analysis of observations of the Orion Molecular Cloud (OMC) and G49.5 (a local HII region). The OMC observations were taken at least once a day to assess the stability of the instrument and demonstrate its on-sky performance. We describe a spectral image processing pipeline to make calibrated maps of raster scans of these sources, incorporating planet observations for gain calibration. We show with G49.5 that, when compared to the Bolocam Galactic Plane Survey, we are able to achieve a $< 3\%$ calibration difference. Based on the outcomes from this commissioning phase of TIME, we have demonstrated preliminary performance, and identified sources of improvement necessary for pursuing a LIM measurement.
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All authors Benjamin J. Vaughan, Abigail T. Crites, Dongwoo T. Chung, Ryan P. Keenan, James J. Bock, Charles M. Bradford, Victoria L. Butler, Tzu-Ching Chang, Yun-Ting Cheng, Audrey Dunn, Nicholas Emerson, Clifford Frez, Jonathon Hunacek, Chao-Te Li, Ian N. Lowe, King Lau, Daniel P. Marrone, Evan C. Mayer, Sophie M. McAtee, Dang Pham, Shwetha Prakash, Guochao Sun, Isaac Trumper, Anthony D. Turner, Ta-Shun Wei, Selina F. Yang, Michael Zemcov

Cosmology and Nongalactic Astrophysics · Cross-listed from physics.flu-dyn

No evidence of vorticity production from irrotational turbulent gravitational collapse yet

Axel Brandenburg, Evangelia Ntormousi and Jennifer Schober

Gravitational collapse creates large amounts of kinetic energy that could potentially seed turbulence. If such turbulence were also suitable to initiate dynamo action, the resulting magnetic field would further modify the dynamics, especially on small length scales. However, a small-scale dynamo is believed to require vortical turbulence, whereas the collapse produces mainly irrotational motions, which may not be efficient for dynamo action. Here, we study the efficiency of vorticity production during a turbulent collapse. We adopt a barotropic equation of state, where pressure and density gradients are parallel, and no magnetic field, so that vorticity can only be produced by viscosity and by vortex dynamo-type amplification. Using direct numerical simulations of gravitational collapse, we show that, for the parameter space accessible to our numerical resolution, these effects are related to the initial irrotational turbulence and are not induced by the collapse. Vorticity production along with the associated small-scale dynamo action are still expected to occur for sufficiently large Reynolds numbers, especially when baroclinic effects are allowed for, but some of the earlier numerical evidence in the literature using a barotropic equation of state is now found to be the result of subgrid scale modeling and not reproduced in direct numerical simulations.
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Cosmology and Nongalactic Astrophysics

Interpretation of the binned SNe Ia Master Sample data via a scalar quintessence component: phantom transition?

Giovanni Montani, Iolanda Navone, Maria Giovanna Dainotti et al. (+1 more)

We study a modified cosmological scenario for the late Universe, involving an evolutionary dark energy model associated with the dynamics of a self-interacting scalar field in a potential-dominated regime. Through the analogy with a fluid energy-momentum tensor, we introduce a viscous contribution to the scalar dynamics, accounting for effective non-equilibrium behaviour of the self-interacting scalar cluster. The resulting picture is that of an intrinsic quintessence contribution which, due to the bulk viscosity, admits an effective equation of state parameter that can also take values below -1. Within this framework, we set up the diagnostic tool of the so-called "effective running Hubble constant", which allows us to trace possible deviations from a standard LambdaCDM model. We then compare this theoretical function with binned data from the Master Sample of Supernovae Ia, constructed assuming a LambdaCDM model in the MCMC procedure performed in each bin. We show that the self-interacting scalar field corresponding to the best fit satisfies a slow-rolling condition, since the kinetic energy remains small compared to the potential contribution throughout the redshift interval. The key finding is that, when limiting the model to specific regions of the parameter space and fitting it to the data, the transition only occurs at redshifts significantly lower than the redshift value identified by the DESI Collaboration. Furthermore, for the parameter values ensuring the best fit, no quintessence-to-phantom transition occurs (i.e., the effective equation of state parameter remains below -1 across the whole redshift domain). In other words, Supernovae data alone provide no indication of a change in the nature of the dark energy.
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All authors Giovanni Montani, Iolanda Navone, Maria Giovanna Dainotti, Shigehiro Nagataki

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Preheating and oscillon formation in Einstein-scalar-Gauss-Bonnet gravity

Areef Waeming, Josu C. Aurrekoetxea, Katy Clough et al. (+2 more)

Non-perturbative processes in the early universe may create overdense structures in scalar fields like the inflaton, called oscillons. In this work, we explore whether the leading order higher derivative contributions to the scalar-tensor theory change the formation and growth of these structures, and investigate the limits in which the effective field theory (EFT) description breaks down. We find that whilst the properties of the oscillons are not significantly modified, and black holes do not generically form, for large couplings the period of formation can result in the evolution leaving the regime of validity of the EFT, at which point predictivity is lost and the next order terms in the EFT should become relevant. If the oscillons survive their formation, they tend to be stable and the EFT corrections remain bounded. The EFT breakdown is triggered by large curvature terms in the metric in the densest regions of the oscillon, meaning that approximations of such modified theories that neglect the local backreaction and non-linear dynamics of the fields may miss important effects.
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All authors Areef Waeming, Josu C. Aurrekoetxea, Katy Clough, Pau Figueras, Áron D. Kovács

Cosmology and Nongalactic Astrophysics

Galaxy Clusters Selected via the Sunyaev-Zel'dovich Effect in 5 year data from the SPT-3G Main Survey

L. E. Bleem, M. Klein, K. Kornoelje et al. (+148 more)

We report a new galaxy cluster catalog, selected using the thermal Sunyaev-Zel'dovich (SZ) effect, from 5 years of observations of the SPT-3G Main field. Drawn from arcminute-resolution data with white noise levels of 3.2, 2.5, and 8.9 $\mu$K-arcmin at 95, 150, and 220 GHz, respectively, the sample consists of 8,892 cluster candidates detected above significance $\xi=4$, with an expected purity of $>82\%$ (4,480 at $\xi\ge5$ with purity $>99\%$). Using optical and infrared data we have confirmed 7,190 candidates as clusters. The sample spans a mass range $7.9 \times 10^{13}$ $M_\odot/h_{70}$ \ $< M_\textrm{500c} < $ $1.6 \times 10^{15}$ $M_\odot/h_{70}$ with a median mass of $1.65 \times 10^{14}$ $M_\odot/h_{70}$, and a redshift range of $0.037<z\lesssim 2$ with a median redshift of $z_{\textrm{med}}$ = 0.73; 1,780 clusters are at $z>1$ and 271 at $z>1.5$. Compared to previous SZ cluster samples from South Pole Telescope and Atacama Cosmology Telescope data, the SPT-3G sample is highly consistent in mass and redshift but is significantly deeper, with per-cluster detection signal-to-noise 2-4 times higher and a cluster density of 4.5 confirmed clusters/deg$^2$. We cross match with eRASS1 cluster and point source catalogs, finding 1,279 and 1,319 matches, respectively. The SPT and eROSITA cluster mass estimates are in relatively good agreement. We perform a series of validation checks using both internal data splits and comparisons to external samples. These tests show increasing correlated (dusty) emission with redshift, with a $\sim17\times$ larger 220 GHz temperature increment for clusters at $z\sim1.5$ than $z\sim0.25$, but only weak evidence for correlated synchrotron emission. Finally, a number of clusters are flagged as candidate strong gravitational lenses.
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All authors L. E. Bleem, M. Klein, K. Kornoelje, S. Bocquet, J. A. Sobrin, M. Aguena, E. Anderes, A. J. Anderson, F. Andrade-Oliveira, B. Ansarinejad, M. Archipley, L. Balkenhol, D. R. Barron, P. S. Barry, M. Bayliss, K. Benabed, A. N. Bender, B. A. Benson, F. Bianchini, F. R. Bouchet, D. Brooks, D. L. Burke, M. Calzadilla, R. Camilleri, E. Camphuis, M. G. Campitiello, J. E. Carlstrom, A. Carnero Rosell, J. Carretero, J. Carron, C. L. Chang, P. M. Chichura, A. Chokshi, T.-L. Chou, A. Coerver, M. Costanzi, T. M. Crawford, L. N. da Costa, C. Daley, T. M. Davis, T. de Haan, J. De Vicente, S. Desai, K. R. Dibert, H. T. Diehl, M. A. Dobbs, M. Doohan, D. Dutcher, S. Everett, G. Evrard, C. Feng, K. R. Ferguson, N. C. Ferree, K. Fichman, B. Flaugher, B. Floyd, K. Fosdick, A. Foster, S. Galli, A. E. Gambrel, A. K. Gao, J. García-Bellido, F. Ge, M. D. Gladders, S. Grandis, F. Guidi, S. Guns, G. Gutierrez, N. W. Halverson, S. R. Hinton, E. Hivon, G. P. Holder, D. L. Hollowood, W. L. Holzapfel, J. C. Hood, A. Hryciuk, N. Huang, T. Jhaveri, S. Kent, F. Kéruzoré, A. R. Khalife, G. Khullar, L. Knox, K. Kuehn, C.-L. Kuo, O. Lahav, K. Levy, Y. Li, A. E. Lowitz, C. Lu, G. P. Lynch, T. J. Maccarone, G. Mahler, A. S. Maniyar, J. L. Marshall, E. S. Martsen, M. McDonald, J. Mena-Fernández, F. Menanteau, M. Millea, R. Miquel, J. J. Mohr, J. Montgomery, J. Myles, Y. Nakato, T. Natoli, R. C. Nichol, V. Novosad, R. L. C. Ogando, Y. Omori, A. Ouellette, Z. Pan, K. A. Phadke, A. A. Plazas Malagón, A. W. Pollak, A. Porredon, K. Prabhu, J. Prat, W. Quan, S. Raghunathan, M. Rahimi, A. Rahlin, C. L. Reichardt, A. K. Romer, M. Rouble, J. E. Ruhl, E. Sanchez, D. Sanchez Cid, T. Schrabback, I. Sevilla-Noarbe, A. C. Silva Oliveira, A. Simpson, T. Somboonpanyakul, A. A. Stark, E. Suchyta, M. E. C. Swanson, C. Tandoi, C. To, C. Trendafilova, J. D. Vieira, A. G. Vieregg, V. Vikram, A. Vitrier, Y. Wan, N. Weaverdyck, J. Weller, N. Whitehorn, W. L. K. Wu, M. R. Young, J. A. Zebrowski, J. Zhan

Cosmology and Nongalactic Astrophysics

The local galaxy distribution does not violate the cosmological principle

Till Sawala

The cosmological principle, which states that the Universe is statistically homogeneous and isotropic on sufficiently large scales, is a foundational assumption of the standard cosmological model. A recent analysis of DESI DR1 galaxy samples reported coherent anisotropic features in the local galaxy distribution extending to gigaparsec scales. If correct, this result would directly contradict the cosmological principle and motivate inhomogeneous cosmologies. Here I analyze the same data and compare them with galaxy distributions predicted by the FLAMINGO cosmological hydrodynamic simulation, performed in the standard $\Lambda$CDM paradigm. I show that the apparent anomaly disappears when the correct comoving distance scale is used and when the observations are compared to mock catalogs that account for bias and redshift-space distortions. Rather than violating the cosmological principle, the observed structures are consistent with those expected in a $\Lambda$CDM Universe.
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